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| United States Patent |
6,158,106
|
|
Ohkura
, et al.
|
December 12, 2000
|
Oxide superconducting wire manufacturing method
Abstract
A long oxide superconducting wire for a coil or a cable, manufacturing
method thereof, an oxide superconducting coil and a cable conductor which
have high operational frequency are provided. The wire is a tape-like
oxide superconducting wire including a plurality of filaments of oxide
superconductor embedded in a matrix, and each filament is twisted spirally
along the longitudinal direction of the tape wire. By winding the wire in
a coil, an oxide superconducting coil is obtained. When a plurality of
such wires are collected, an oxide superconducting cable conductor can be
obtained.
| Inventors:
|
Ohkura; Kengo (Osaka, JP);
Sato; Kenichi (Osaka, JP)
|
| Assignee:
|
Sumitomo Electric Industries, Inc. (JP)
|
| Appl. No.:
|
739908 |
| Filed:
|
October 30, 1996 |
Foreign Application Priority Data
| Aug 02, 1993[JP] | 5-191374 |
| Aug 10, 1993[JP] | 5-198626 |
| Dec 28, 1993[JP] | 5-336852 |
| Current U.S. Class: |
29/599; 257/E39.018; 505/431; 505/433 |
| Intern'l Class: |
H01L 039/24 |
| Field of Search: |
29/599
505/100,431,433,704,740
|
References Cited
U.S. Patent Documents
| 4885273 | Dec., 1989 | Sugimoto et al. | 29/599.
|
| 4952554 | Aug., 1990 | Jin et al. | 29/599.
|
| 4954479 | Sep., 1990 | Dubots et al. | 29/599.
|
| 4988669 | Jan., 1991 | Dersch | 505/704.
|
| 5004722 | Apr., 1991 | Tallman | 29/599.
|
| 5043320 | Aug., 1991 | Meyer et al. | 29/599.
|
| 5045527 | Sep., 1991 | Ikeno et al. | 505/740.
|
| 5063200 | Nov., 1991 | Okada et al. | 505/704.
|
| 5081075 | Jan., 1992 | Jin et al. | 29/599.
|
| 5132278 | Jul., 1992 | Stevens et al. | 505/704.
|
| 5424282 | Jun., 1995 | Yamamoto et al. | 29/599.
|
| Foreign Patent Documents |
| 503525 A1 | Mar., 1992 | EP.
| |
| WO 89/02656 | Mar., 1989 | WO.
| |
Primary Examiner: Bryant; David P.
Attorney, Agent or Firm: Pennie & Edmonds LLP
Parent Case Text
This is a continuation, of application Ser. No. 08/282,347, filed Jul. 29,
1994, now abandoned.
Claims
What is claimed is:
1. A method of manufacturing a superconducting coil formed of an oxide
superconducting wire, comprising the following sequence of steps:
heat treating a powder mainly consisting of an oxide superconducting
material;
covering said powder with a metal sheath;
drawing said covered powder to form a single-filamentary wire;
providing a metal or metal alloy having a resistance value at a room
temperature higher than that of said metal sheath and in a range of
10.sup.-6 to 10.sup.-8 .OMEGA.m on a surface of said single-filamentary
wire;
putting then as-obtained single-filamentary wires together to form a
multi-filamentary wire;
drawing said multi-filamentary wire;
rolling said multi-filamentary wire;
heat treating said multi-filamentary wire; and
winding said multi-filamentary wire to become said coil.
2. The method of manufacturing an oxide superconducting wire according to
claim 1, wherein
in the steps of drawing and rolling after said multi-filamentary wire is
prepared, after drawing, the as-obtained wire having a circular cross
section is twisted.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a superconducting wire and manufacturing
method thereof, as well as to an oxide superconducting coil and a cable
conductor. More specifically, the present invention relates to an oxide
superconducting wire, manufacturing method thereof, an oxide
superconducting coil and a cable conductor having high critical current
density and low a.c. loss.
2. Description of the Background Art
In recent years, superconducting materials of ceramics, i.e., oxide
superconducting materials, are watched with interest due to higher
critical temperatures thereof. Among these materials, yttrium, bismuth and
thallium oxide superconducting materials which exhibit high critical
temperatures of about 90K, 110K and 120K respectively, are expected for
practical application.
A single-filamentary oxide superconducting wire having high critical
current density formed of such oxide superconducting materials is obtained
by heat treating and then covering with a metal sheath the material
powder, drawing, rolling and by further heat treatment. Similarly, an
oxide superconducting multi-filamentary wire having high critical current
density is obtained by heat treating powder mainly consisting of oxide
superconducting material, then covering the same with a metal sheath,
drawing and putting together the as-obtained wires to provide a
multi-filamentary wire, and further by drawing, rolling and heat treating
the same.
It has been conventionally known that an oxide superconducting wire having
higher critical current density can be obtained by repeating several times
the steps of rolling and heat treatment in manufacturing such an oxide
superconducting wire.
If such an oxide superconducting wire is to be applied to an a.c. cable or
magnet, it must have low a.c. loss, high strength and superior property
under bending-strain, in addition to the high critical current.
The single-filamentary and the multi-filamentary oxide superconducting
wires manufactured through the conventional method described above have as
high a critical density as 30000 A/cm.sup.2 or higher.
However when an a.c. current is applied with the wire wound in a coil,
there is generated an a.c. loss heat radiation. This is because an induced
current flows between the metal sheath and the ceramics when an a.c.
current is applied, resulting in heat radiation caused by a.c. loss of
normal conduction resistance of the metal sheath, as compared to the case
when a d.c. current is applied, in which case current flows only through
the ceramic portions. Since the temperature of the coil as a whole
increases, critical current density is decreased.
Accordingly, the operational frequency of the coil manufactured in
accordance with the conventional method has been about 0.1 Hz at the
highest.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above described problems
and to provide a long oxide superconducting wire for a coil or a cable,
manufacturing method thereof, an oxide superconducting coil and a cable
conductor which have high operational frequency.
Another object of the present invention is to provide a long oxide
superconducting wire for a coil or a cable, manufacturing method thereof,
an oxide superconducting coil and a cable conductor having high
operational frequency and high strength.
A further object of the present invention is to provide a long oxide
superconducting wire for a coil or a cable, manufacturing method thereof,
an oxide superconducting coil and a cable conductor having high
operational frequency and superior property under bending-strain.
According to one aspect of the present invention, an oxide superconducting
wire is provided, which wire is a tape-like oxide superconducting wire
including a plurality of filaments of oxide superconductor embedded in a
matrix, with the filament twisted spirally along the longitudinal
direction of the tape wire.
As mentioned above, the filament of oxide superconductor embedded in the
matrix is twisted spirally along the longitudinal direction of the wire.
Therefore, the induced current flowing between the matrix and the filament
is cut at every twist pitch and flows in a small loop, so that the
magnitude of the current is limited. As a result, heat radiation caused by
a.c. loss of the matrix can be avoided. This function will be discussed in
detail with reference to the figures.
FIG. 8 is a perspective view showing a conventional oxide superconducting
multi-filamentary wire.
Referring to FIG. 8, the multi-filamentary wire is constituted by filaments
11a, 11b, 11c and 11d of oxide superconductor embedded in a silver matrix
2.
When the multi-filamentary wire structured in this manner experiences a
change in the magnetic field dB/dt generated, for example, by a coil,
there is generated a large induced current loop 13 other than the applied
current between filaments 11a and 11b because of an induced electromotive
force, and therefore a large loop current I flows. Accordingly, heat
radiation derived from the superconducting resistance of silver matrix 2
increases in proportion to (dB/dt).sup.2 with the frequency.
By contrast, FIG. 7 is a perspective view showing an oxide superconducting
multi-filamentary wire of one example of the present invention.
Referring to FIG. 7, the multi-core wire is constituted by filaments 1a,
1b, 1c and 1d of oxide superconductor embedded in silver matrix 2, with
each of the filaments 1a, 1b, 1c and 1d twisted spirally along the
longitudinal direction of the multi-filamentary wire.
When the multi-filamentary wire structured in this manner experiences the
change in the magnetic field dB/dt, the induced current loop 3 is limited
by the length L.sub.p of the twist pitch of the filaments 1a and 1b.
Consequently, the magnitude of loop current I.sub.p also decreases, and
the a.c. loss decreases as the length L.sub.p of the twist pitch
decreases.
Preferably, the pitch of the twist should be at least the width of the
wire. This prevents disconnection of the wire during twisting, rolling and
drawing.
Preferably, the matrix may be silver or silver alloy, since the matrix of
silver or silver alloy can serve as a stabilizer. The a.c. loss mentioned
above is in reverse proportion to the resistance value of the matrix. In
order to reduce the a.c. loss, it is preferable to provide a matrix having
high resistance, by using silver alloy.
According to another aspect of the present invention, an oxide
superconducting wire is provided which is similar to the wire of the
aforementioned aspect and additionally characterized in that each of the
plurality of filaments is covered by silver or silver alloy, and a barrier
layer of metal or metal alloy having the resistance value at a room
temperature higher than that of silver alloy and in the range of 10.sup.-6
to 10.sup.-10 .OMEGA.m is provided to surround one or more filaments
covered by silver or silver alloy in the longitudinal direction of the
wire.
More preferably, the barrier layer should be formed of metal or metal alloy
having the resistance value at a room temperature in the range of from
10.sup.-7 to 10 .sup.-9 .OMEGA.m.
As described above, a barrier layer of high resistance is provided to
surround the filament in the longitudinal direction of the wire is
provided. The barrier layer may be provided thin over the surface or at
the interface between the oxide superconducting material and the metal
sheath before the single-filamentary wires are put together, and as it
experiences work hardening during the subsequent steps of drawing,
twisting and rolling, disconnection is not caused. In addition, since the
barrier material experiences appropriate work hardening, tensile strength
and bending strength of the finished tape are improved, and therefore an
oxide superconducting wire, which has high strength and high resistance
against high electromagnetic stress when it is wound into a coil and
current is applied, can be obtained.
According to a still another aspect of the present invention, an oxide
superconducting coil is provided which is formed of a tape-like oxide
superconducting wire including a plurality of filaments of oxide
superconductor embedded in a matrix, with each filament twisted spirally
along the longitudinal direction of the tape wire. In the superconducting
wire structured in this manner, heat radiation caused by the a.c. loss of
the matrix is reduced as already described. Therefore, a coil having high
operational frequency can be obtained.
In accordance with a still another aspect of the present invention, an
oxide superconducting cable conductor is provided, which is formed of a
tape-like oxide superconducting wire including a plurality of filaments of
oxide superconductor embedded in a matrix, with each filament being
twisted spirally along the longitudinal direction of the tape wire. In the
superconductor wire structured in this manner, heat radiation caused by
a.c. loss of the matrix is reduced as already described. Therefore, a
cable conductor having high operational frequency can be obtained.
According to a still further aspect of the present invention, a method of
manufacturing an oxide superconducting wire is provided which includes the
steps of heat treating and then covering with a metal sheath, powder
mainly consisting of oxide superconducting material, drawing and putting
together the as-obtained wires to provide a multi-filamentary wire,
drawing and rolling, and heat treating, in which in the step of drawing
and rolling after the wires are put together to provide a
multi-filamentary wire, each as-obtained wire with circular cross section
is drawn, twisted and then rolled.
According to this method, by this twisting, the induced current flowing
between the metal sheath and the ceramics is cut at every pitch of the
twist and flows in a small loop, so that the magnitude of the current is
limited and heat radiation caused by the a.c. loss of the metal sheath can
be avoided. Therefore, operational frequency when the wire is applied to a
coil or a cable in the conventional manner can be increased. The twisting
is effected after the material powder is covered by the metal sheath,
drawn, put together to provide a multi-filamentary wire and again drawn,
before rolling. Therefore, there is not an irregularity of filaments
inside after rolling, and therefore, rolling can be carried out easily.
A technique for reducing surface of a shielded current loop by twisting
filaments in a metal supercoducting wire having circular cross section has
been disclosed in Yamamura et al. Chodendo Kogaku (Superconductivity
Engineering) 1974, pp. 64-66.
However, the present invention is directed to a very thin tape-like oxide
superconducting wire. According to the present invention, it becomes
possible to twist the filaments in the tape-like wire by twisting the wire
while it has circular cross section and then rolling.
Preferably, after the wires are twisted, the wires should be again drawn
and rolled.
Since the wires are drawn, then twisted and again drawn, swells of the
wires generated during the twisting process can be eliminated. Therefore,
after rolling, there is not snaking of the tape, and the tape can be
uniformly rolled. There is not a possibility of untwisting of the
filaments in the tape.
Preferably, the pitch of the twist after rolling should be made at least
the width of the wire after rolling. If the twist pitch is made equal to
or larger than the tape width after rolling, the wire is not disconnected
during the steps of twisting, rolling and drawing.
More preferably, the angle of inclination at the step of twisting after
rolling should be made at least 0.5.degree. with respect to the direction
of the wire. If the twisting is effected in this range, the filament
simply has its arrangement directly changed in the longitudinal direction,
and therefore uneven processing of the filament is prevented. Further,
since the filament is arranged at an angle with respect to the
longitudinal direction of the tape because of the twist, the
bending-strain of the filament when the tape is bent can be reduced as a
result. Therefore, property under stain of the tape with respect to the
critical current can be improved when the tape is twisted. If the angle of
twist is smaller than 0.5.degree., the effect of twisting is not obtained,
and this effect can be obtained if the angle is 0.5.degree. or larger.
The angle of inclination here refers to the maximum angle .alpha. of the
filament 51 positioned at the outermost layer of the wire and the center
line 50 along the longitudinal direction of the wire.
According to a still further aspect of the present invention, a method of
manufacturing an oxide superconducting wire is provided which includes the
steps of heat treating and then covering with a metal sheath, powder
mainly consisting of an oxide superconducting material, drawing and
putting together the as-obtained wires to provide a multi-filamentary
wire, drawing and rolling, and heat treating, in which a metal or metal
alloy having resistance value at a room temperature higher than that of
the metal sheath and in the range of 10.sup.-6 to 10.sup.-10 .OMEGA.m is
provided at the surface of the as-obtained single filamentary wire or
between the oxide superconducting material and the metal sheath, before
the single filamentary wires are put together to provide the
multi-filamentary wire.
More preferably, the metal or metal alloy deposited at the surface of the
single-filamentary wire or at the interface between the oxide
superconducting material and the metal sheath has a resistance value at a
room temperature in the range of 10.sup.-7 to 10.sup.-9 .OMEGA.m.
In this manner, a barrier layer of metal or metal alloy having high
resistance is provided at the surface of the single-filamentary wire or at
the interface between the oxide superconducting material and the metal
sheath. The barrier of high resistance disposed between the filaments may
be provided thin over the surface or at the interface between the oxide
superconducting material and the metal sheath before the
single-filamentary wires are put together. Since the barrier experiences
work hardening during the subsequent steps of drawing, twisting and
rolling, disconnection is not caused. Further, since the barrier material
experiences appropriate work hardening, tensile strength and bending
strength of the finished tape are improved, and therefore an oxide
superconducting wire which has high strength and high resistance against
high electromagnetic stress when it is wound into a coil and current is
applied thereto, can be obtained.
Preferably, in the steps of drawing and rolling after the wires are put
together to provide a multi-filamentary wire, the as-obtained wire having
the circular cross section is drawn and twisted. By twisting the wire in
this manner, the heat radiation caused by the a.c. loss of the metal
sheath can be avoided, as already described.
As described above, according to the present invention, an oxide
superconducting wire with low a.c. loss can be obtained. Therefore, the
oxide superconducting wire manufactured in accordance with the present
invention can be applied to an oxide superconducting magnet or cable
operated at a high frequency including power frequency of 0.1 Hz or
higher, and it can be also applied widely to various coils for a.c. motors
such as induction motors, synchronous motors, as well as for transformers,
and to large-capacity a.c. cable conductors.
Further, according to the present invention, an oxide superconducting wire
which has not only the low a.c. loss but also high strength and superior
property under stain can be obtained.
It is difficult to reduce the twist pitch in actual manufacturing. However,
when silver alloy is used, similar characteristic effect as obtained when
the twist pitch is reduced, can be obtained.
The foregoing and other objects, features, aspects and advantages of the
present invention will become more apparent from the following detailed
description of the present invention when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 3 show steps of manufacturing an oxide superconducting wire in
accordance with the present invention.
FIG. 4 is a perspective view showing the oxide superconducting wire of one
example of the present invention.
FIG. 5 is a cross section schematically showing the structure of the oxide
superconducting wire shown in FIG. 4.
FIG. 6 is a cross section schematically showing the structure of the oxide
superconducting wire of another example of the present invention.
FIG. 7 is a perspective view showing an oxide superconducting
multi-filamentary wire of an example of the present invention.
FIG. 8 is a perspective view showing a conventional oxide superconducting
multi-filamentary wire.
FIG. 9 illustrates the angle of inclination of the superconducting wire in
accordance with the present invention.
FIG. 10 shows a structure of an apparatus for measuring the a.c. loss of
the oxide superconducting wire.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The oxide superconducting wire, superconducting coil and manufacturing
method thereof in accordance with the present invention will be described.
EXAMPLE 1
Bi.sub.2 O.sub.3, PbO, SrCO.sub.3 , CaCO.sub.3 and CuO were mixed to have
the composition ratio of Bi:Pb:Sr:Ca:Cu=1.81:0.40:1.98:2.21:3.03. The
mixed powder was successively subjected to heat treatments in the ambient
atmosphere at 750.degree. C. for 12 hours, 800.degree. C. for 8 hours, and
in a reduced pressure atmosphere of 1 Torr, at 760.degree. C. for 8 hours.
After each step of heat treatment, the powder was pulverized. The power
obtained through the heat treatment and pulverization was further
pulverized by a ball mill, and powder of sub micron order was obtained.
The powder was subjected to heat treatment at 800.degree. C. for 2 hours,
and filled in a metal pipe having the outer diameter of 12 mm and inner
diameter of 9 mm.
The powder filled in the silver pipe was drawn to 1 mm and thus a strand
was fabricated. Thereafter, a plurality of stands 4 were put together and
inserted in a metal pipe having the outer diameter of 12 mm and inner
diameter of 9 mm, and a multi-filamentary wire having 61 filament was
obtained, as shown in FIG. 1. Then, as shown in FIG. 2, the wire was
further drawn until it has the diameter of 1.0 mm. Referring to FIG. 2,
the multi-filamentary wire obtained in this manner consisted of 61
filaments 7 of superconducting material embedded in a matrix 6 of silver.
Then, referring to FIG. 3, the as-obtained multi-core wires after drawing,
which had circular cross section, were twisted to have the twist pitch of
500 mm, 100 mm, 50 mm and 10 mm, respectively, and then lightly drawn to
the diameter of 0.98 mm.phi.. The wires were rolled to have the tape width
of 3.0 mm and the thickness of 0.22 mm, and heat treatment was effected at
850 .degree. C. for 50 hours. Thereafter, the wires were further subjected
to rolling until it had the thickness of 0.20 mm, and further heat
treatment at 850 .degree. C. for 50 hours.
FIG. 4 is a perspective view showing the oxide superconducting wire of one
example of the present invention obtained in this manner.
Referring to FIG. 4, the oxide superconducting wire consists of 61
filaments of oxide superconductor in a matrix 2 of silver. The filament 1
is twisted spirally along the longitudinal direction of the wire.
FIG. 5 is a cross section schematically showing the structure of the oxide
superconducting wire shown in FIG. 4. Referring to FIG. 5, the oxide
superconducting wire includes filaments 1 of oxide superconductor embedded
in a matrix 2 of silver. Matrix 2 serves as a stabilizer.
In the similar manner, wires having different twist pitches were prepared,
and respective wires were cut to have the length of 40 mm, critical
current density Ic of respective cut wires were measured, and the
influence of the twisting on the Ic was studied.
As a result, critical currents were 21 A, 20 A, 19 A and 17 A in the wires
having the twist pitches of 500, 100, 50 and 10 mm, respectively. Though
the critical current decreased slightly as the pitch was made smaller, it
was not significantly reduced. The results were when a d.c. current was
applied.
In this manner, four long oxide superconducting wires having the length of
13 m and different twist pitches were fabricated, and the obtained wires
were wound in the shape of pancakes. The coil had the outer diameter of
100 mm .phi., inner diameter of 40 mm.phi. and the height of 6 mm. Four
coils were fabricated, using superconducting wires having mutually
different twist pitches.
The a.c. loss in the coils obtained in this manner was measured and
compared by using an apparatus such as shown in FIG. 10. The method of
measurement will be discussed in detail.
Referring to FIG. 10, by using an a.c. power supply 30, an a.c. current was
applied to a coil 31 in liquid nitrogen filled in a cryostat 32. The
effective value i.sub.IN of the a.c. current was 5 A and a frequency f was
50 Hz. The coil voltage v.sub.out and the coil current i.sub.OUT generated
at both ends of the coil 31 at this time were measured. In order to remove
the voltage of inductance and to measure only the resistance component,
the coil voltage v.sub.OUT was measured in accordance with the 0.degree.
phase output voltage of a lock-in amplifier 33. The coil current was
measured by using an a.c. voltmeter 34.
By using the coil current value and the coil voltage value obtained in this
manner, the a.c. loss was calculated in accordance with the following
equation:
a.c. loss=(coil effective current value).times.(coil voltage).
As a result of the measurement, the a.c. loss was 210 mW, 170 mW, 130 mW
and 20 mW in the wires having the twist pitch of 500, 100, 50 and 10 mm,
respectively.
As is apparent from the result, the a.c. loss decreases remarkably as the
twist pitch is reduced.
Meanwhile, a long oxide superconducting wire having the length of 50 m was
fabricated under the same condition as above except that it was not
twisted after drawing. The obtained wire was wound in a double pancake in
the similar manner and the a.c. loss was measured in the similar manner,
which was 300 mW.
From the above, it can be understood that when a long wire is manufactured,
if the wire is twisted after drawing in the steps of drawing and rolling,
the a.c. loss of the coil employing the wire, can be significantly
reduced.
The inventors tried to fabricate a wire having the length of 50 m and the
twist pitch of smaller than 10 mm, for example 3 mm. However, during the
step of twisting, the wire was disconnected at several portions, and such
twisting was impossible.
Therefore, actually, it is necessary to make the twist pitch not smaller
than the tape width.
EMBODIMENT 2
Bi.sub.2 O.sub.3, PbO, SrCO.sub.3, CaCO.sub.3 and CuO were mixed to have
the composition ratio of Bi:Pb:Sr:Ca:Cu=1.81:0.40:1.98:2.21:3.03. The
mixed powder was successively subjected to heat treatments in an ambient
atmosphere at 750.degree. C. for 12 hours, 800.degree. C. for 8 hours and
in a reduced pressure atmosphere of 1Torr, at 760.degree. C. for 8 hours.
At the end of each heat treatment, the powder was pulverized. The powder
obtained through such heat treatment and pulverization was further
pulverized by a ball mill, and the powder of sub micron order was
obtained. The powder was subjected to heat treatment at 800.degree. C. for
2 hours, and then filled in a silver pipe having the outer diameter of 12
mm and the inner diameter of 11 mm.
Further, a pipe of silver with 10% of gold added having the outer diameter
of 12.3 mm.phi. and the inner diameter of 12 mm.OMEGA. was provided
outside the silver pipe.
The powder filled in the double pipes was drawn to 1 mm, and the
as-obtained wires were put together and inserted in a silver pipe having
the outer diameter of 12 mm and the inner diameter of 9 mm, to provide a
multi-filamentary wire having 61 filaments. This wire was further drawn to
have the diameter of 1.0 mm.
The multi-filamentary wires after drawing which had circular cross section
were twisted to have the twist pitch of 500 mm, 100 mm, 50 mm and 10 mm,
respectively and lightly drawn to have the diameter of 0.98 mm.phi.. The
as-obtained wires were rolled to have the thickness of 0.22 mm, and then
subjected to heat treatment at 850.degree. C. for 50 hours.
FIG. 6 is a cross section showing the structure of the oxide
superconducting wire in accordance with this another example of the
present invention obtained in this manner.
Referring to FIG. 6, the oxide superconducting wire includes filaments 1 of
oxide superconductor embedded in a matrix 2 of silver. Around the filament
1, a barrier layer 8 of silver with 10% gold added is provided,
surrounding the filament 1.
In this manner, wires having different twist pitches were fabricated, and
the wires were cut to have the length of 400 mm. Critical current Ic of
each of the wires was measured, and the influence of twisting on the Ic
was studied.
As a result, the critical currents were 21 A, 20 A, 19 A and 17 A in the
wires having the twist pitches of 500, 100, 50 and 10 mm, respectively,
and Ic was not significantly reduced, though slightly reduced as the pitch
was made smaller. The results were when a d.c. current was applied.
Four oxide superconducting multi-filamentary wires having the length of 12
m and mutually different twist pitches were fabricated, and the obtained
wires were wound in the shape of pancakes. Each coil has the outer
diameter of 100 mm.phi., the inner diameter of 40 mm.phi. and the height
of 6 mm. Four coils were fabricated using superconducting wires having
mutually different twist pitches.
The a.c. loss of the coils obtained in this manner was measured and
compared by using the apparatus such as shown in FIG. 10, as in Example 1.
More specifically, a.c. current having the effective value of 5 A and
frequency of 50 Hz was applied to the coil in liquid nitrogen, only the
resistance component of the voltage generated at both ends of the coil was
detected in accordance with the 0.degree. phase signal of the lock-in
amplifier, and the a.c. loss was compared.
As a result, the a.c. loss was 74 mW, 40 mW, 27 mW and 3 mw in the wires
having the twist pitches of 500, 100, 50 and 10 mm, respectively.
As is apparent from the result, the a.c. loss remarkably reduces as the
twist pitch is made smaller.
Meanwhile, a long oxide superconducting wire having the length of 50 m was
prepared under the same condition as above, except that it was not twisted
after drawing and high resistance barrier was not provided. The obtained
wire was wound in the shape of a double pancake in the similar manner, and
the a.c. loss was measured, which was 300 mW.
From the above, it is understood that when a long wire is manufactured, in
the steps of drawing and rolling, if the wire is drawn and then twisted,
the a.c. loss of the coil employing the wire can be significantly reduced.
EXAMPLE 3
Bi.sub.2 O.sub.3, PbO, SrCO.sub.3 , CaCO.sub.3 and CuO were mixed to have
the composition ratio of Bi:Pb:Sr:Ca:Cu=1.81:0.40:1.98:2.21:3.03. The
mixed powder was successively subjected to heat treatments in the ambient
atmosphere at 750.degree. C. for 12 hours, 800.degree. C. for 8 hours and,
in a reduced pressure atmosphere of 1 Torr, at 760.degree. C. for 8 hours.
At the end of each heat treatment, the powder was pulverized. The powder
obtained through the heat treatment and pulverization was further
pulverized by a ball mill, and the powder of the sub micron order was
obtained. The powder was subjected to heat treatment at 800.degree. C. for
2 hours, and then filled in a silver pipe having the outer diameter of 12
mm and the inner diameter of 9 mm.
The powder filled in the silver pipe was drawn to 1 mm, and the as-obtained
wires were put together into a silver pipe having the outer diameter of 12
mm and the inner diameter of 9 mm, to provide a multi-filamentary wire
having 61 filaments. The as-obtained wire was further drawn to have the
diameter of 1.0 mm.
The multi-filamentary wires after drawing were twisted to have the twist
pitches of 500 mm, 100 mm, 50 mm and 10 mm, respectively, and lightly
drawn to have the diameter of 0.98 mm.phi.. The resulting wires were
rolled to have the tape width of 3.0 mm and the thickness of 0.22 mm, and
then subjected to heat treatment at 850.degree. C. for 50 hours.
Thereafter, the wires were further drawn to have the thickness of 0.20 mm,
and subjected to heat treatment at 850.degree. C. for 50 hours.
Thereafter, the wires having different twist pitches were cut to have the
length of 40 mm, critical current Ic thereof was measured, and the
influence of the twisting on the Ic was studied.
As a result, the critical currents were 21 A, 20 A, 19 A and 17 A in the
wires having the twist pitches of 500, 100, 50 and 10 mm, respectively,
and Ic was not significantly reduced, though it was slightly lowered as
the pitch was made smaller. The results were when a d.c. current was
applied.
The twist angles of the wires having the twist pitches of 500, 300, 200 and
100 mm were studied, which were 0.30.degree., 0.5.degree., 0.9.degree. and
1.7.degree., respectively. By using these tapes, property under strain of
the Ic was studied at the bending diameter of 20 mm.
The influence of the twist pitch was studied in accordance with the ratio K
(K=Ic/Ic.sub.0) of the Ic (Ic.sub.0) before bending and Ic after bending,
the value K was 0.7, 0.85, 0.9 and 0.9 for the twist angle of
0.30.degree., 0.50.degree., 0.9.degree.and 1.7.degree., respectively. It
was recognized that the property under stain was improved as the twist
angle increased. It was found that the effect was obtained when the angle
was made at least 0.5.degree..
Four long oxide superconducting multi-filamentary wires having the length
of 13 m and twist pitches of 500, 100, 50 and 10 mm, respectively were
fabricated, and the resulting wires were wound in the shape of pancakes.
Each coil has the outer diameter of 100 mm.phi., the inner diameter of 40
mm.phi. and the height of 6 mm. Four coils were fabricated, using
superconducting wires having mutually different twist pitches.
The a.c. loss of the coils obtained in this manner was measured and
compared by using an apparatus such as shown in FIG. 10, as in Embodiment
1. More specifically, an a.c. current having the effective value of 5 A
and the frequency of 50 Hz was applied to the coil in liquid nitrogen, and
only the resistance component of the voltage generated at both ends of the
coil was detected in accordance with the 0.degree. phase signal of the
lock-in amplifier, and the a.c. loss was compared.
As a result, the a.c. loss of the wires having twist pitches of 500, 100,
50 and 10 mm was 190 mW, 180 mW, 120 mW and 10 mW, respectively.
As can be understood from the result, the a.c. loss was reduced remarkably
as the twist pitch was made smaller.
A long oxide superconducting wire having the length of 50 m was fabricated
under the same conditions as above except that it was not twisted after
drawing. The resulting wire was wound in a double pancake in the similar
manner and the a.c. loss was measured in the similar manner, which was 300
mW.
It is understood from the foregoing that when a long wire is manufactured,
in the steps of drawing and rolling, if the wire is twisted after drawing,
it comes to have superior bending characteristics, less degradation of Ic
and the a.c. loss of the coil can be significantly reduced, when the wire
is wound into a coil.
EXAMPLE 4
Bi.sub.2 O.sub.3 , PbO, SrCO.sub.3, CaCO.sub.3 and CuO were mixed to have
the composition ratio of Bi:Pb:Sr:Ca:Cu=1.81:0.40:1.98:2.21:3.03. The
mixed powder was successively subjected to heat treatments in the ambient
atmosphere at 750.degree. C. for 12 hours, 800.degree. C. for 8 hours and
in a reduced pressure atmosphere of 1 Torr, at 760.degree. C. for 8 hours.
At the end of each heat treatment, the powder was pulverized. The powder
obtained through the heat treatment and pulverization was further
pulverized by a ball mill, and the powder of sub micron order was
obtained. The powder was heat treated at 800.degree. C. for 2 hours, and
filled in an alloy pipe of silver to which 10% gold was added, having the
outer diameter of 12 mm and the inner diameter of 9 mm.
The powder filled in the silver alloy pipe was drawn to 1 mm, and the
as-obtained wires were put together and inserted into an alloy pipe of
silver and 10% gold having the outer diameter of 12 mm and the inner
diameter of 9 mm, to provide a multi-filamentary wire having 61 filaments.
The wire was further drawn to the diameter of 1.0 mm.
The multi-filamentary wires after drawing, which had circular cross section
were twisted to have the twist pitches of 500 mm, 100 mm, 50 mm and 10 mm,
respectively, and lightly drawn to 0.98.phi.. The as-obtained wires were
rolled to have the thickness of 0.22 mm and subjected to heat treatment at
850.degree. C. for 50 hours. Thereafter, the wires were further rolled to
have the thickness of 0.20 mm and subjected to heat treatment at
850.degree. C. for 50 hours. Thereafter, wires having different twist
pitches were cut to have the length of 400 mm, the critical current Ic of
the wires was measured, and the influence of the twist on the Ic was
studied.
As a result, the critical currents were 21 A, 20 A, 19 A and 17 A in the
wires having twist pitches of 500, 100, 50 and 10 mm, and Ic was not
significantly reduced, though it was slightly decreased as the pitch was
made smaller. The results were when a d.c. current was applied.
In this manner, four long oxide superconducting multi-filamentary wires
having the length of 13 m and mutually different twist pitches were
fabricated, and the resulting wires were wound in the shape of pancakes.
Each coil has the outer diameter of 100 mm.phi., the inner diameter of 40
mm.phi. and the height of 6 mm. Four coils were fabricated using
superconducting wires of mutually different twist pitches.
The a.c. loss of the coils obtained in this manner was measured and
compared by using an apparatus such as shown in FIG. 10, as in Example 1.
More specifically, an a.c. current having the effective value of 5 A and
frequency of 50 Hz was applied in liquid nitrogen, and only the resistance
component of the voltage generated at both ends of the coil was detected
in accordance with the 0.degree. phase signal of the lock-in amplifier,
and the a.c. loss was compared.
As a result, the a.c. loss was 80 mW, 35 mW, 33 mW and 5 mW in the wires
having the twist pitches of 500, 100, 50 and 10 mm, respectively.
As is apparent from the results, the a.c. loss was significantly reduced as
the twist pitch was reduced.
A long oxide superconducting wire having the length of 50 m was fabricated
under the same conditions as above except that it was not twisted after
drawing. The obtained wire was wound similarly in a double pancake, and
the a.c. loss was measured, which was 300 mW.
It is understood from the foregoing that when a long wire is manufactured,
in the steps of drawing and rolling, if the wire is twisted after drawing,
the a.c. loss of the coil can be significantly reduced when the wire is
wound into a coil.
EXAMPLE 5
By using the tape-like superconducting wire covered by a metal sheath in
accordance with the present invention, a small coil having the
specification shown in Table 1 below was fabricated and the a.c conduction
characteristics was studied in accordance with the conduction conditions
specified in Table 2. Silver or silver with 10% Au added thereto was used
as the metal sheath. The twist pitch was 20 mm and 50 mm, and a wire which
was not twisted was also fabricated for comparison.
TABLE 1
______________________________________
Coil Specification
______________________________________
coil inner diameter
20 mm.phi.
outer diameter
40 mm.phi.
height 12 mm
double pancake
2
tape wire sheath metal Ag or Ag +10% Au
width 2.7 mm
thickness 0.72 mm
length 3m/double pancake
______________________________________
TABLE 2
______________________________________
Conduction Condition
______________________________________
frequency 30Hz
applied current 10A
peak magnetic field .+-.321 gauss
temperature of measurement
77K (in liquid nitrogen)
______________________________________
The result of measurement of the a.c. loss measured by using the apparatus
shown in FIG. 10 as in Example 1 is as shown in Table 3 below.
TABLE 3
______________________________________
a.c. loss
when Ag was used
when Ag +10% Au was
twist pitch
for metal sheath
used for metal sheath
______________________________________
20 mm 100 mW 10 mW
50 mm 150 mW 20 mW
not twisted
200 mW 70 mW
______________________________________
By collecting a plurality of oxide superconducting wires fabricated in the
manner as described above, an oxide superconducting cable conductor can be
obtained.
The present invention can be applied not only to the manufacture of a
bismuth superconducting wire but also to manufacture of thallium and
yttrium superconducting wires.
Although the present invention has been described and illustrated in
detail, it is clearly understood that the same is by way of illustration
and example only and is not to be taken by way of limitation, the spirit
and scope of the present invention being limited only by the terms of the
appended claims.
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